Method for producing impregnated



Patented June 10, 1952 METHOD FOR PRODUCING IMPREGNATED CARBON BRUSHES Melville *F. Peters and Anne BrPeters, Newark, N. J.

No Drawing.

Original application August 3, 1945,

.Serial No. 608,826. Divided and this application April 15, 1948, Serial No. 21,306

3 Claims.

(Granted under the act of March a, 1883, as

. amended April 30, 1928; 370 0. G. 757) Rapid wear of carbon brushes has been known for sometime to occur at sea level in dry air. More recently, it has been found that brushes also wear rapidly at high altitudes due to the usually dry atmosphere up there. Laboratory tests have shown that many kinds of brushes wear rapidly at reduced pressures not only in dry air but even in moist air. This indicates that at high altitudes these brushes wear rapidly regardless of the atmospheric humidity. Such rapid wear has made direct current motors and generators hazardous at high altitudes under any conditions. Accordingly, for the last few years, many agencies and manufactures have carried on work to determine the causes and remedy for this wear.

Numerous methods have been devised to overcome this wear by impregnating the brushes with various compounds in difierent ways. The present invention deals with one such method which has been found not only to increase thelifeof carbon brushes but also to improve their performance and .to make it possible to control their voltage drop characteristic between brush and commutator to suit requiredments.

One of the objects of this invention, is therefore, to treat carbon brushes in such manner as to increase their life by decreasing wear.

Another object is to provide a method of treatment of carbon brushes whereby their voltage drop between brush and commutator may be predetermined as desired.

Another object is to decrease brush wear and improve commutation level by introducing compounds such as silver sulfide.

Another object is to provide a method for impregnating carbon brushes with insoluble compounds by gradual precipitation from soluble compounds in which the brushes are first soaked, by immersing them in a solution containing the precipitant.

Other and more specific objects will appear in the following description.

Impregnation of carbon brushes with AgzS has been found to increase their life considerably and to alter the voltage drop across the brushes to the commutator. The AgzS may be precipitated from AgNO3, in which the brushes are first soaked, by submerging them then in water containing H28, or in (NH4)2S. The reaction of the ammonium sulfide is as follows:

If water containing HzS is used for the precipitation the voltage drop is lowered, whereas, if

2 (NI-102$ is used, the voltage drop is increased. Thus any desired drop within this range may be predetermined by using more orless of either precipitant to get the desired voltage drop to suit any particular requirements.

necessary lubrication at the higher temperatures produced by the higher potential drop at the commutator by the Ag2S precipitated in this method.

Other comparatively insoluble compounds may be introduced in the brushes for the purpose of inhibiting brush wear in a similar manner, by first soaking the brushes in a solutionof a soluble compound from which the insoluble compound may then be precipitated by immersing them in a solution of another soluble compound. For example, it has been found that lead iodide and bismuth acetate are good wear inhibitors and may be precipitated in the brushes by first soaking them in a solution of lead acetate and then submerging them in a solution of tbismuth iodide, or vice versa. The precipitation is caused by the following reaction:

The process of precipitation in the above reactions is sufficiently gradual to permit a practically homogeneous precipitation throughout the mass of the carbon brushes. To ensure a more homogeneous precipitation the brushes may be thoroughly dried after soaking in the first solution so as to permit better permeation of the second solution through all the pores of the brushes before the initial precipitation clogs the pores nearer the surface to prevent continuation of the process further inwardly of the carbon mass.

The time required for soaking the brushes in the solutions obviously depends on the porosity of the carbon, a more porous material requiring less time for thorough saturation. Saturation may also be hastened by first placing the carbon brush in a reduced pressure chamber to partially evacuate the pores therein, then soaking it in the solution under normal or super-atmospheric pressure. Likewise, the evacuation step might be 3 omitted and the soaking done under a higher pressure.

It is to be understood that normally the copper oxide formed on the commutator at ordinary operating temperatures acts as a smooth coating to reduce wear of the brushes which would otherwise wear much faster on a copper surface. The

copending application Serial No. 608,826, filed August 3, 1945, now abandoned, for Carbon Brushes which is a division of our patent applieration is obtained. Hence, in some cases of operation under conditions which might cause an excessive range of temperatures, it is necessary to provide more lubrication of a type which will maintain a good lubricating film at the higher temperatures where copper oxide and the AgzS is not sufficient to keep the temperature below the range of boiling or decomposition of the lubricants. It is, therefore, a question of introducing the proper ingredients in the proper proportions and in a manner to get the desired results under the conditions of operation encountered. The methods herein outlined make it possible to provide a proper treatment of carbon brushes to give maximum wear for any given set or range of operating conditions.

Thus it is possible to:

1. Control the voltage drop between the brush and commutator.

2. Decrease brush wear for a range of operating brush temperatures by introducing a series of compounds which decompose over the same range of temperatures.

3. Decrease brush wear and improve the commutation level by introducing compounds such as 7 silver sulfide.

cation Serial No. 493,790, filed July 7, 1943, for Carbon Brushes, which has matured into Patent No. 2,428,036 on September 30, 1947.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A method of impregnating porous carbon brushes with lead iodide comprising soaking them in lead'acetate solution, then soaking them in a solution of bismuth iodide so as to precipitate lead iodide within the pores.

2. A method of treating porous carbon brushes comprising soaking them in a solution of lead acetate, then soaking them in a solution of bismuth iodide in alcohol whereby to precipitate lead iodide within the pores of said brushes.

3. A method of treating porous carbon brushes comprising soaking them in a solution of lead acetate, allowing said solution to dry within the pores of the brushes, then soaking them in a solution of bismuth iodide inalcohol whereby to precipitate lead. iodide within the pores o;f said brushes.

MELVILLE F. PETERS. ANNE B. PETERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Roscoe 8: Schorlemmer, Treatise on Chemistry, Macmillan & Co. Ltd., London 1907, vol. II, page 873, lines 2, 3 and 4. 

1. A METHOD OF IMPREGNATING POROUS CARBON BRUSHES WITH LEAD IODIDE COMPRISING SOAKING THEM IN LEAD ACETATE SOLUTION, THE SOAKING THEM IN A SOLUTION OF BISMUT IODIDE SO AS TO PRECIPITATE LEAD IODIDE WITHIN THE PORES. 